The invention concerns new O-benzyl-N-hydroxyalkyl derivatives of chitosan, as well as nail polish containing these compounds.
The essential characteristics which should distinguish a good nail polish are sufficient hardness, good applicability (ease of application), short drying period, high storage stability (i.e. the nail polish should maintain its homogeneity and a good stability over a long time period), resistance against light, water, washing agents and rinsing agents, as well as, above all, harmlessness to skin and nails. Finally, the nail polish should provide a polish film with satisfactory characteristics. The characteristics expected of such a nail polish film are uniform thickness, high luster, prerequisite for which is a smooth surface, outstanding adhesiveness to the keratin of the nails, and a good elasticity. Good elasticity avoids breaks in the polish and also avoids its peeling off.
Nail polish contains, in general, a film-former, a resin component and a solvent system, as well as, if necessary, softeners, pigments and customary additives.
Typically, nail polishes contain nitro-cellulose as film-former. Particularly preferred herewith are estersoluble nitro-celluloses (so-called E-collodium wool or "RS"-nitro-cellulose) with moderate to low viscosity. Nail polish based upon nitro-cellulose possesses, however, a number of disadvantages: thus, for example, with the use of nitro-cellulose, discolorations of the nail polish occur in the course of time. Moreover, nitro-cellulose tends to display sudden changes in viscosity, which makes more difficult a uniform application of the nail polish. In addition, it must be noted that the nitro-cellulose employed in nail polishes is neutral, i.e. free of acid components. A content of free acid can lead, namely, to not only an injury to the finger nails and the skin, but also to decomposition of the dyes contained in the nail polish.
It is also known that nitro-cellulose, on account of its high degree of inflammability and explosiveness, must be manufactured and handled with the greatest care.
In order to obtain satisfactory results with regard to adhesiveness, luster and hardness of the nail polish, the modern combination polishes based upon nitro-cellulose must be supplemented with various other resin components. Coming into consideration in this connection are, in addition to natural polymers such as e.g. shellac, elemi gum and, particularly, colophonium, synthetic resins, such as for example, polystyrene, polyvinyl acetate and polymethacrylic acid ester, e.g. polypropyl methacrylate and polymethyl methacrylate. Moreover, alkyde resins, such as e.g. polymerizates of phthalic acid anhydride and glycerin, as well as formaldehyde/urea-resins and, preferably, arylsulfonamide/rormaldehyde-resins, such as e.g. a polymer produced from equimolar amounts of formaldehyde and p-toluene sulfonamide, which is known by the designation Santolite.sup.R, are employed.
It has been proven many times that one can avoid the above-mentioned disadvantages through the use of synthetic copolymers, such as e.g. copolymerizates of hydrophobic and hydrophilic monomer units (see, e.g. EP-OS No. 00 85 370), instead of nitro-cellulose as film-former in nail polishes. Moreover, reference is made to the German Offenlegungsschriften DE-OS No. 31 12 888 and DE-OS No. 32 05 545.
Despite all of the previous difficulties in producing a nitro-cellulose-free nail polish, and whether or not a nail polish film based exclusively on nitro-cellulose cannot satisfy the mentioned requirements and are first made more hard, more adhesive, more elastic and more resistant by means of addition of further resin components, these film-formers represent, now as berore, unavoidable components of many nail polishes. It has not been possible, namely, to develop nitro-cellulose-free nail polishes which provide, in all of the characteristics essential for nail polish, equally good or indeed better results than nail polish based upon nitro-cellulose. Thus, for example, with the above mentioned nail polishes based upon synthetic polymers, problems can arise on account of the physiological effect of possible present traces of monomer, which are removable from the polymerizate only with great difficulty.
In contrast hereto, the chitin alkyl ester suggested for use as film-former in nail polishes in DE-OS No. 35 37 333 is physiologically urobjectionable. However, this chitin alkyl estercan only be obtained by means of a complicated and expensive process. In particular, the production of high molecular, sufficiently substituted chitin alkyl esters, which can also form closed film surfaces without addition of softeners, is only possible under considerable technical expenditure and precise reaction conditions at 0.degree. C.